A law in Arizona that the ACLU is calling "the most extreme and dangerous of abortion bans" was blocked from taking effect on Thursday after an emergency appeals request.

Arizona was set to become the ninth state to forbid doctors from aborting a fetus 20 weeks into a pregnancy. But unlike elsewhere in the country, Arizona would start the 20-week count after a pregnant woman's last menstrual period, or about 18 weeks into a pregnancy -- which is typically before medical problems can be detected in fetuses in prenatal exams, according to a lawsuit filed by the ACLU and the New York-based Center for Reproductive Rights.

The law, which the U.S. Ninth Circuit Court of Appeals blocked on Wednesday, will likely be on hold through at least October, when all briefs on the case will be filed, said Julie Rikelman, litigation director for the Center for Reproductive Rights. A final decision is likely to be made in November or December, she said.

"We're thrilled with the decision," Rikelman said. "It's really great news for women in Arizona. We're very excited that women will still be able to get the health care that they need."